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The causes of seasonal changes in numbers of the yellow dung fly, Scathophaga stercoraria (Diptera: Scathophagidae)
Author(s) -
GIBBONS D. S.
Publication year - 1987
Publication title -
ecological entomology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.865
H-Index - 81
eISSN - 1365-2311
pISSN - 0307-6946
DOI - 10.1111/j.1365-2311.1987.tb00996.x
Subject(s) - biology , pupa , breed , zoology , larva , ecology
. 1. Counts of adult Scathophaga stercoraria (L.) on cow pats were made in Houghall, County Durham, in 1964 and 1965. 2. A spring peak of numbers was due to adults (overwintered mainly as pupae or larvae) maturing and going to dung to breed. Numbers then dropped, rising to one or more peaks in late June—early July. In 1964 there was then a summer drop in numbers until late September. In 1965 high numbers persisted in summer associated with cooler, wetter weather. Autumn peaks in both years persisted until severe frosts or snow. 3. Mature adults, developed from eggs laid during the spring peak, form the first generation when breeding in mid‐late June. No clear generations can be identified after this, due to eggs being laid daily (females have successive gonotrophic cycles). Changes in adult numbers breeding reflects survival of eggs and newly‐hatched larvae 5–6 weeks earlier, and lower survival rates of adults in mid‐summer compared with spring and autumn. 4. Adult Scathophaga numbers in vegetation rose as numbers on dung dropped. Females dissected to count ovariole tunica dilatations showed that most flies in vegetation were immature, with some parous flies hunting insects to develop the next batch of eggs. 5. Females on dung were dissected and found to range from immature to seven‐parous. Those gravid for the first time were grossly under‐represented, possibly due to wider dispersal. 6. It is suggested that seasonal changes in this r‐strategist cannot be explained simply in terms of generations nor by the occurrence of adult diapause.